if you mix middleburn and shimano,it will never be possible to set up correctly.
shimano design all three rings,front mech,chain etc to work as well as possible. as soon as you mix and match then the amount of front mech cable pull for certain gear combos will never match up to the new position of this chainring thats been added.the centering of each of the new chainring/and or the thickness in certain areas will be a little diffrent to a set up than with 3 shimano rings.not to mention the problem you are currently having.
aftermarket rings can wear well and look lovely.. but once you mix in a 32t made by middleburn and attempt to set up the cable tension etc to get it functioning exactly how you had it before,you can pick out the small diffrences by looking closely as you change gear slowly on the workstand. (yes, fire through all the gears fast and you wont notice.quick,get it off the workstand and get the customer out the door as quick as you can why dont you - nice one.)
its not just the once.this has been the case for as long as i can remember.you mix and match then you have to accept slight diffrences and to be fair,its not just some of middleburns rings.these are diffrences that might not ever cause a problem but are diffrences that are one step backwards from the best shimano could come up with in the first place.
Then you will find folk that dont care about the small diffrences,some will say they dont notice a thing.these folk will want hard wearing rings that will shift well.they can accept that they arent quite as good as shimano.not the best,but they will shift well.
give a gear crunching beginner a mix and match set up and you will more often than not find them having problems as they dont know how to shift cleanly to dodge the problem. If you want good wearing rings up front then at least fit all three middleburns.if you want the best shifting,althought it might not last anywhere near as long,fit shimano.
we fit soft compound tyres and soft grips but how often do folk moan about them wearing out too soon? sometimes,but you are more likely to hear praise on how well they enhanced the ride for the short time they were in use.
Its a pity folk dont have the same views on their drive.